1. Field of the Invention
This invention relates generally to the field of video surveillance systems. More specifically, it relates to an image forming and processing device including a fisheye lens having a substantially hemispherical field of view. The invention allows an operator to view a selected part of the image formed by the fisheye lens as if it were formed by a normal lens by simulating the panning, tilting or zooming of the normal lens. This allows the operations of panning, tilting and zooming to be implemented without the use of moving parts.
2. Description of Related Art
Surveillance cameras are commonly used to monitor areas of retail stores, factories, airports and the like. In order to use a single camera to survey a large area, the camera is typically provided with mechanisms to enable it to pan, tilt and zoom. Such mechanisms increase the complexity and hence the cost of the camera and can also adversely affect its reliability. Due to the presence of moving parts, mechanical pan, tilt and zoom devices are subject to damage and degradation brought on by extremes of temperature, moisture and dust. In addition, such mechanical systems consume relatively large amounts of power. A surveillance camera capable of panning, tilting and zooming without the use of moving parts would therefore provide significant advantages over existing surveillance cameras.
In U.S. Pat. No. 5,185,667, Zimmermann proposes such a camera having no moving parts. In the device specified in that patent, a fisheye lens is coupled to a video camera such that the camera produces an electronic image. Due to the characteristics of the fisheye lens, the image is distorted. The distortion in the image is corrected by means of an algorithm.
One of the limitations of the system proposed by Zimmermann is that the camera is unable to provide sufficient resolution for effective zooming. Since a fisheye lens renders a distorted image of an entire hemisphere, parts of the image, especially at its peripheries are distorted. The image is formed on a change coupled device (CCD) having a limited number of pixels. In order to view the image as a normal (non-distorted) image, it is necessary to transform the image electronically. The limited number of pixels in the CCD causes the transformed image to be poorly resolved. In order to provide acceptable resolution, a CCD made of approximately 156,000,000 would be needed.
The best available CCD's have approximately 16,000,000 pixels (4,000.times.4,000) and operate at clocking rates of the order of 10 Mhz. However, in order to satisfy the NTSC sampling rate of 30 samples per second, a clocking rate of 480 MHz is needed. Thus, the type of resolution required for an NTSC picture with the desired magnification cannot be achieved using the prior art.
In U.S. Pat. No. 5,200,818, Neta et al. describe a system in which a wide angle scene is monitored by means of a plurality of sensor arrays mounted on a generally hemispherical surface. Each sensor array has its own lens system. This allows a wide field to be monitored without the need for moving parts to effect panning and tilting. The resolution of the system would be relatively high due to the plurality of sensor arrays. However a system such as that described by Neta et al. would be very costly to implement due to the large number of high quality components needed.
It is an object of the present invention to provide a surveillance camera apparatus, having a substantially hemispherical field of view and capable of effecting the operations of panning, zooming and tilting without the use of moving parts, while still providing sufficient resolution to allow the desired magnification.
It is a further object of the invention to provide a surveillance camera apparatus, having a substantially hemispherical field which allows an operator to view parts of the field of view as if they were acquired by a camera having a conventional lens and being capable of panning, tilting and zooming.
These and other advantages are achieved by the invention described herein.